Existing microelectronic device packages typically include a microelectronic substrate or die attached to a support member, such as a printed circuit board. Bond pads or other terminals on the die are electrically connected to corresponding terminals on the support member, for example, with solder balls. The connection between the die and the support member can be encapsulated, for example, with a protective underfill material, to form a device package. The package can then be electrically connected to other microelectronic devices or circuits, for example, in a consumer or industrial electronic product such as a computer.
In one existing arrangement shown in FIG. 1, a package 10 can include a support member 20 that carries a microelectronic die 30. Solder balls 50 provide an electrical connection between upwardly facing bond pads of the support member 20 and downwardly facing bond pads of the die 30. Accordingly, a gap (partially filled by the solder balls) is initially formed between the support member 20 and the die 30.
In one existing process, an underfill material 40 is initially disposed adjacent to two of the outer edges of the die 30. The underfill material 40 flows into the gap between the die 30 and the support member 20 to provide a protective encapsulant around the solder balls 50. The underfill material 40 can flow both directly into the gap (as indicated by arrows A) and around the outer edges of the die 30 (as indicated by arrows B).
One characteristic the process described above with reference to FIG. 1 is that in some cases, the underfill material 40 can flow more quickly around the die 30 (arrows B) than directly into the gap beneath the die 30 (arrows A). Accordingly, the underfill material 40 can trap air or other gases in the gap. A drawback with this arrangement is that the gases within the gap may expand when the temperature of the package 10 is elevated, causing the electrical connections provided by the solder balls 50 between the die 30 and the support member 20 to fail.
One existing approach for addressing the foregoing drawback is to control the viscosity of the underfill material 40 so that it preferentially wicks more quickly through the gap than around the periphery of the die 30. For example, the viscosity can be controlled by controlling the temperature at which the underfill process is conducted, or the concentration of particulates in the underfill material 40. Alternatively, the surface characteristics of the die 30 and/or the support member 20 can be selected to produce a faster underfill flow rate through the gap than around the periphery of the die 30. Although the foregoing methods can produce satisfactory results, it may in some cases be difficult and/or expensive to accurately control the aforementioned variables. Furthermore, the underfill material 40 typically provides a permanent bond between the die 30 and the support member 20, making it difficult if not impossible to replace a defective die 30 without destroying the entire package 10.